Smart cards employed in mobile applications are usually equipped with internal voltage controllers by which an internal power is supplied thereto without being significantly affected by external noises or internal changes of operation modes.
In general, such smart cards for mobile applications are designed to provide low power operation. Accordingly, an internal voltage controller of a smart card may be designed to provide relatively low current operations. An operating speed of an internal voltage controller may be proportional to an amount of current consumed therein. However, such a low-power internal voltage controller may not be sufficiently quick to respond to external noise or internal changes of operation modes.
FIG. 1 is a circuit diagram showing a conventional internal voltage generator.
Referring to FIG. 1, the internal voltage controller 10 includes a comparator 11, a driver 12 and a voltage divider 13. The voltage divider 13 operates to divide an internal voltage Vint on a node N1 through resistors R1 and R2. A divided voltage Vfed (hereinafter, referred to as ‘feedback voltage’) is provided to the comparator 11. The comparator 11 operates to compare the feedback voltage Vfed with the reference voltage Vref. The driver 12 is controlled responsive to a result of the comparison. The driver 12 generates the internal voltage Vint from an external voltage Vext responsive to control of the comparator 11. The internal voltage Vint is provided to internal circuits 20, 30, and 40, and the internal voltage Vint is maintained at about a predetermined level by the internal voltage controller 10. The predetermined level of the internal voltage Vint is a target voltage level.
When the external voltage Vext varies due to noise or operation mode changes in the internal circuits 20, 30, and 40, the internal voltage Vint may vary. If the internal voltage Vint is reduced, the feedback voltage Vfed is reduced. The comparator 11 operates to compare the lowered feedback voltage Vfed with the reference voltage Vref, and to generate a result of the comparison. The driver 12 is turned on responsive to the result of the comparison, to supply an external current Iext to the internal circuits 20, 30, and 40, so that the internal voltage Vint increases in level. The internal voltage Vint rises until the feedback voltage Vfed is equal to the reference voltage Vref.
If the feedback voltage Vfed reaches the reference voltage Vref, the driver 12 is turned off responsive to the comparator 11, and then, the external current text to the internal circuits 20, 30, and 40 is turned off. Thus, the internal voltage Vint does not increase further. Accordingly, the internal voltage Vint is maintained at about a target voltage level using the internal voltage controller 10. When the internal voltage Vint increases above the target voltage level, the internal voltage controller 10 operates to turn off the external current Iext so that the internal voltage Vint is reduced. As a result, the internal voltage controller 10 maintains the internal voltage Vint at about the target voltage regardless of external or internal change in voltage or operation mode.
The internal voltage controller 10 is generally designed to be operable with relatively low power consumption. For that reason, the internal voltage controller 10 may not rapidly respond to variation of external noises or internal operation modes. For example, if the internal voltage Vint becomes lower in level due to variation of external noises or internal operation modes, the internal voltage controller 10 may raise the internal voltage Vint up to the target voltage level. The low-power internal voltage controller 10, however, may not operate at fast speed. Thus, while the internal voltage Vint is increasing to the target voltage level, the internal circuits 20, 30, and 40 may not operate in a normal condition because they may not be supplied with sufficient currents.
When the internal voltage Vint increases due to variation of external noises or internal operation modes, the internal voltage controller 10 reduces the internal voltage to the target voltage level. The internal voltage controller 10, however, may not operate at high speed because it is designed to be operable at low power. Thus, while the internal voltage Vint decreases to the target voltage level, the internal circuits 20, 30, and 40 may be stressed by excessive current conditions because they are supplied with too much current. Although accelerating an operation speed of the internal voltage controller 10 may reduce aforementioned problems of the internal voltage controller 10, an amount of current consumed may increase undesirably. The internal voltage controller 10 with high current consumption may be undesirable for a mobile-specific smart card.